1. Field of the Invention
The present invention relates to a vehicle power transmission apparatus for use with a belt type stepless speed change device to transmit the torque of an electrically activated driving source to the driven side of the vehicle. The apparatus minimizing the changes in the variable speed characteristic which are caused primarily by the varying frictional resistance due to time induced belt wear. Thus, the comfort of the passenger(s) is maintained on board a smoothly operating vehicle.
2. Description of Background Art
Of the vehicles driven by an internal combustion engine or by an electric motor, some employ a belt type stepless speed change device as the automatic transmission for smoothly transmitting the torque of the driving source to the driven side of the vehicle. For example, Japanese Patent Laid-Open No. 3-128789 discloses an electrically driven vehicle including a belt type stepless speed change device. This stepless speed change device has an endless belt with a trapezoid cross section engaged between the driving pulley mounted on the motor output shaft on the one hand, and the driven pulley furnished on the reduction gear input shaft on the other.
When engaged frictionally, the endless belt of the above cross-sectional shape transmits the torque across the driving pulley to the driven pulley. Over time, the coefficient of friction of the pulleys varies due primarily to secular change. In particular, the intermediate speed characteristic between high and low speeds is liable to change. The changed intermediate speed characteristic deteriorates the quality of the transmission apparatus or causes the performance thereof to become erratic. The irregularities often detract from the comfort of the passenger(s) on board the vehicle operating with the transmission apparatus in question.